Process for decontamination of hardening salt residue

ABSTRACT

Decontamination of hardening salt residues is accomplished by treating the large pieces broken and slurried in water with an iron-II-chloride solution equivalent to the cyanide portion at a pH of 7-14, in the presence of at least the equivalent amount of alkali carbonate corresponding to the alkaline earth present, wherein the alkali carbonate does not exceed 30% based on the contaminated hardening salt residue.

United States Patent [1 1 Reinhardt et al.

[451 Feb. 11,1975

1 1 PROCESS FOR DECONTAMINATION OF HARDENING SALT RESIDUE [76] Inventors: Helmut Reinhardt, Am Dem Stumpelrott 9, 5038 Rodenkirchen; Karl Trebinger, Josef-Zimmermann-Strasse 7; Gottfried Kallrath, Nordstrasse 51, both of 5047 Wesseling; Helmut Weber, Stettiner Strasse 8, 5040 Bruhl, all of Germany [22] Filed: June 19, 1973 [21] Appl. No.: 371,498

[30] Foreign Application Priority Data June 30, 1972 Germany 2232123 [52] US. Cl 423/164, 423/165, 423/186, I 423/367, 210/53 [51] Int. Cl C0lc 3/12, COlf 1/00 [58] Field of Search 423/155, 158, 161, 164, 423/165, 367,140, 143, 236, 658.5, 1;

[56] References Cited UNITED STATES PATENTS 1,315,219 9/1919 Espenhahn 423/236 1,604,565 10/1926 Coulier 423/236 3,226,182 12/1965 Martino 423/236 3,695,833 10/1972 Wiedeman et al 423/633 X 3,764,659 10/1973 Reinhardt 423/236 Primary Examiner-Edward J. Meros Assistant Examiner-Brian E. Hearn Attorney, Agent, or Firm-Cushman, Darby & Cushman ABSTRACT 7 Claims, No Drawings PROCESS FOR DECONTAMINATIQN OF HARDENING SALT RESIDUE In industrial processes the problem of poisonous waste products and their recovery is of continually inever, this is' not possible in all cases as, for example, in

the most important areas of steel hardening.

In the steel working industry known hardening salts are added in order to impart specific properties to the workpieces by annealing, hardening, tempering, carburizing or nitriding. The salts added for this purpose generally include alkali chlorides, e.g., sodium chloride and potassium chloride, alkali cyanides, e.g., sodium cyanide and potassium cyanide, alkali cyanates, e.g., sodium cyanate and potassium cyanate, alkali nitrites, e.g., sodium nitrite and potassium nitrite, alkali nitrates, e.g., sodium nitrate and potassium nitrate, alkali carbonates, e.g., sodium carbonate and potassium carbonate and alkaline earth salts such as barium carbonate, strontium chloride, barium chloride, strontium carbonate, calcium carbonate, magnesium carbonate, calcium chloride, and magnesium chloride.

From time to time the salt baths must be renewed or be replaced by fresh baths whereupon used up hardening salts results. These salts whose main components 1 are cyanides and barium compounds cannot be removed by depositing them becauseof their high toxicity. This is aggravatedv because the residues not only are very toxic themselves but besides occur not only in a few large scale operations but instead occur in many, partially small plants.

An environmentally favorable process for making these salts innocuous must be economical. The previously known processes on the contrary are very expen' sive.

According to one of these processes the cyanide salts for example are converted into hydrocyanic acid and this is then burned catalytically. According to another process there is formed from the hydrocyanic acid formate which can be deposited only at high cost. In both cases, however, the entire unused cyanide present is lost (M. Schindewolf, Ein neues Verfahren zur Vernichtung von CyanidAbfallen, Chem. lng. Techn. 44 (1972) 682).

Besides in this type of working up there results mixtures of heavy metal salts with alkali and alkaline earth salts whose destruction presents the same problems as the hardening salt residues themselves.

It is the idea of the present application to develop a working up process in which the main components of the hardening salt residue, namely barium and cyanide (e.g., present as barium chloride or barium carbonate and sodium cyanide or potassium cyanide) are recovered in a valuable form. The depositing of large amounts of mixtures of heavy metal and alkali or alkaline earth salts also is avoided.

It has now been found that the barium and cyanide components of hardening bath residues (such as the residues of baths containing the compounds set forth above) can be recovered if the salt residue which has been broken down in normal size pieces and slurried in water is treated with an aqueous iron (II) chloride solution at a pH of 7 to 14 in an amount equivalent to the cyanide portion of the residue and in the presence of the least amount of alkali carbonate, e.g., sodium carbonate or potassium carbonate corresponding to alkathere can be used soda or-potash. Soda is preferred since it is frequently already present in the hardening I salt residue. It is preferably added in solid form. The concentration of iron (II) chloride in the water ist not critical. Conveniently it is employed as a 5 to 40 so lution.

The resulting precipitate contains the alkaline earth carbonates, i.e., also magnesium carbonate; the filtrate on the contrary contains the alkali ferrocyanide formed as well as alkali cyanate and alkali chloride.

The carbonate percipitate and the filtrate are worked up separately.

The carbonate precipitate after washing with water is dissolved in a mineral acid, preferably hydrochloric acid, and by the addition of barium hydroxide the ,en-

tire alkaline earth ions with the exception of barium ions were precipitated as hydroxide and separated from barium. The hydroxides can be deposited directly with suitable precautions or after conversion to thesulfates. The resulting, pure barium. chloride solution can be worked up in known manner, for example, in a spray drier or crystallizer.

The filtrate which contains the alkali ferrocyanide after acidification with a mineral acid, e.g., hydrochloric acid whereby carbon dioxide develops, precipitates as Berlin white upon further addition of iron (II) chloride and can be worked up in known manner with alkali cyanide, e.g., sodium cyanide or potassium cyanide to the corresponding alkali ferrocyanide, e.g., sodium fer rocyanide or potassium ferrocyanide. In this way no further waste water problem occurs. In the strongly alkaline pH range of 9-14 the nitrite or nitrate portion can be reduced to ammonia, if more FeCl is added, as

' is necessary for reaction of the cyanide. The hardening bath residue is broken to the usual granule size, preferably to 2 to 5 mm. Finely divided material to be sure is more easily decomposed but requires higher grinding costs, while with coarse grained material long reaction times are needed in the decomposition.

This pre-broken salt is then slurried, preferably in 2 /2 times its amount of water. The exact amount of water is not critical. For example it can be 1 to 10 times the amount of broken salt.

The iron (II) salt solution can, if necessary also be added in a somewhat larger than the equivalent amount, namely in an excess up to about 10%. The individual concentrations of the iron (II) salt solution, the alkali carbonate solution and the mineral acid are those of commerce and preferably are about grams of material per liter of solution but can be varied widely.

The industrial advantage of the process of the invention is not only the effective decontamination of the hardening salt residues but also, in the recovery of the main components, barium and cyanide.

Unless otherwise indicated all parts and percentages are by weight.

EXAMPLE A hardening salt residue of the following composition was decontaminated:

BaCl 40% NaCN NaCl 22% Na CO NaOCN 2.5% SrCl CaCI MgCl; 1% NaNO; 1% NaNO l% H O 2.5%

lOO kg of the hardening salt residue was broken into particles of 2-5 mm and introduced into 250 liters of water. With stirring the mixture was heated to the boiling point and treated with 50 liters of waste acid from a pickling bath 128 grams FeCI /l There were added 14 kg of 50 weight of soda lye. After a few minutes no free cyanide can be detected. The wash water can be used for slurrying the next charge.

The precipitate was dissolved in l65 liters of 10 weight hydrochloric acid. By the addition of 3 kg of solid Ba(OH the excess acid was neutralized and all of the alkaline earth metals except the barium precipitated. The precipitate formed was filtered off and the filtrate neutralized with hydrochloric acid. The clear solution was evaporated in a spray drier.

The filtrate from the carbonate precipitate was acidified with 10 weight hydrochloric acid. Thereupon there was observed a strong development of CO lron (ll) ferrocyanide was precipitated by the addition of iron (ll) chloride at a pH of 2. The precipitate was washed in known manner and worked up to potassium ferrocyanide.

What is claimed is:

l. A process of decontaminating a hardening salt residue from treating steel with a hardening salt contain ing alkaline earth metal at least a part of which is barium and also containing cyanide and alkali chloride containing alkaline earth metal at least a part of which is barium and also containing cyanide comprising slurrying the coarsely broken pieces of salt residue in water and then treating said slurry with an amount of aqueous iron (ll) chloride at least sufficient to convert the cyanide portion of said residue to alkali ferrocyanide at a pH of 7-14 and in the presence of alkali carbonate in an amount at least sufficient to convert all of the alkaline earth metal present to the carbonate but not over 30% based on hardening salt residue to be decontaminated, and separating the cyanide containing solution from the carbonate containing precipitate.

2. A process according to claim 1 wherein the pH is 9-14.

3. A process according to claim 1, wherein the alkali carbonate employed is soda.

4. A process according to claim I, wherein the iron (ll) chloride solution is added as the waste acid from pickling.

5. A process according to claim 1 comprising dissolving the carbonate precipitate in mineral acid, adding barium hydroxide in an amount sufficient to precipitate all of the alkaline earth metals present except the barium as the corresponding hydroxides and separating the alkaline earth hydroxide precipitate from the barium containing filtrate.

6. A process according to claim 5 wherein the mineral acid is hydrochloric acid.

7. A process according to claim 1 including the steps of separating the cyanide in solution as iron (ll) ferrocyanide by acidifying the solution and adding iron (ll) chloride to precipitate the iron ferrocyanide. 

1. A PROCESS OF DECONTAINING A HARDENING SALT RESIDUE FROM TREATING STEEL WITH A HARDENING SALT CONTAINING ALKALINE EARTH METAL AT LEAST A PART OF WHICH IS BARIUM AND ALSO CONTAINING CYANIDE AND ALKALI CHLORIDE CONTAINING ALKALINE EARTH METAL AT LEAST A PART OF WHICH ID BARIUM AND ALSO CONTAINING CYANIDE COMPRISING SLURRING THE COARSELY BROKEN PIECES OF SALT RESIDUE IN WATER AND THEN TREATING SAID SLURRY WITH AN AMOUNT OF AQUEOUS IRON (II) CHLORIDE AT LEAST SUFFICIENT TO CONVERT THE CYANIDE PORTION OF SAID RESIDUE OF ALKALI FERROCYANID AT A PH OF 7-14 AND IN THE PRESENC OF ALKALI CARBONATE IN AN AMOUNT AT LEAST SUFFICIENT TO CONVERT ALL OF THE ALKALINE EARTH METAL PRESENT TO THE CARBONATE BUT NOT OVER 30% BASED ON HARDENING SALT RESIDUE TO BE DECONTAMINATED, AND SEPARATING THE CYANIDE CONTAINING SOLUTION FROM THE CARBONATE CONTAINING PRECIPITATE.
 2. A process according to claim 1 wherein the pH is 9-14.
 3. A process according to claim 1, wherein the alkali carbonate employed is soda.
 4. A process according to claim 1, wherein the iron (II) chloride solution is added as the waste acid from pickling.
 5. A process according to claim 1 comprising dissolving the carbonate precipitate in mineral acid, adding barium hydroxide in an amount sufficient to precipitate all of the alkaline earth metals present except the barium as the corresponding hydroxides and separating the alkaline earth hydroxide precipitate from the barium containing filtrate.
 6. A process according to claim 5 wherein the mineral acid is hydrochloric acid.
 7. A process according to claim 1 including the steps of separating the cyanide in solution as iron (II) ferrocyanide by acidifying the solution and adding iron (II) chloride to precipitate the iron ferrocyanide. 